It is known in the prior art to provide a propulsion control system which uses resistors connected in series with one or more DC traction motors to control the acceleration of a transit car. This has been accomplished with a cam controller, which selectively shorts out each of a first plurality of resistors during the acceleration phase of the vehicle control operation and selectively shorts out each of a second plurality of resistors during the brake phase, as disclosed in U.S. Pat. No. 3,218,537. This was mechanically done by respective sets of power contact tips that are located around a rotating shaft on which is placed a series of cam lobed devices. As the shaft rotates, different sets of contact tips are made and broken to accomplish the electrical connections that are required to do the desired resistor shorting. The cam shaft was rotated by an air cylinder through a rack and pinion gear arrangement.
A stepping motor has been known in the prior art for several years, and has the ability to rotate a shaft to a specific desired angular position as a result of a specific number of input pulses that are supplied to the windings of the stepping motor. This gives accurate control to provide a desired angular motion of the motor and the coupled shaft, without requiring feedback signals and circuitry to control the angular position that is desired.
In addition it is known to utilize a microprocessor to control the operation of chopper propulsion apparatus for transit vehicles as disclosed in U.S. Pat. No. 4,282,466 of T. C. Matty. A microprocessor has been provided for operation with the Washington Metropolitan Area Transit Authority or WAMATA cam propulsion system, as disclosed in a U.S. patent application, filed Apr. 29, 1983 and Ser. No. 489,983, by A. Sahasrabudhe et al., but the microprocessor is functioning to determine the speed maintaining and program stop input signals that are supplied to a conventional air cylinder positioned cam propulsion system.
It is known in the prior art to provide an electric motor driven cam propulsion control apparatus, including an electric pilot motor to drive the cam and which is a regular DC motor. A DC pilot motor must be told to turn, it must also be told to stop, and there is required for this purpose an elaborate feedback circuit to properly determine the actual rotational position of that DC pilot motor.